1. Field of the Invention
This invention relates to a controller for controlling a drive source of a construction machine such as, for example, a power shovel and the like, and also controlling energy recovery.
2. Description of the Related Art
Techniques of generating electric power by the use of a return flow from an actuator or the like to rotate a generator have been widely known. One of them recovers energy produced by a rotation motor during braking to rotate a generator.
A hybrid structure in a construction machine such as a power shovel uses, for example, an excess output of an engine to rotate a generator for generation of electric power which is then accumulated in a battery. Then, the power of the battery is used to drive an electric motor in order to actuate an actuator. Also, discharge energy from the actuator is used to rotate the generator for generation of electric power which is similarly then accumulated in the battery. Then, the power of the battery is used to drive the electric motor for actuation of the actuator.
[Patent Literature 1] JP-A 2000-136806
[Patent Literature 2] JP-A 2002-275945
All energy produced by a rotation motor during braking is inertial energy. Disadvantageously, recovery of the inertial energy without runaway of the rotation motor is attended with difficulties. This is because, due to high inertial energy of the rotation motor, inadequate control of recovery of inertial energy leads to runaway likely occurring in the rotation motor, resulting in a high risk. On the other hand, if great weight is given to prevention of runaway of the rotation motor, it gives rise to another disadvantage of insufficient energy recovery.
Another disadvantage is a large energy loss occurring during a long process in which the excess output of the engine and the discharge energy of the actuator which is operated by fluid pressure are regenerated for use to operate the actuator.
Yet another disadvantage is that, since the actuator is operated by the electric motor, if a failure occurs in, for example, an electric system, the entire controller becomes disabled.